67b54c6670
Auto-detect longest common dir in lowerdir option and compact it if the option size is hitting one page size. If does, Use chdir + CLONE to do mount thing to avoid hitting one page argument buffer in linux kernel mount. Signed-off-by: Wei Fu <fhfuwei@163.com>
120 lines
3.0 KiB
Go
120 lines
3.0 KiB
Go
/*
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Copyright The containerd Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package sys
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import (
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"runtime"
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"syscall"
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"unsafe"
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"github.com/pkg/errors"
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"golang.org/x/sys/unix"
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)
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// FMountat performs mount from the provided directory.
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func FMountat(dirfd uintptr, source, target, fstype string, flags uintptr, data string) error {
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var (
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sourceP, targetP, fstypeP, dataP *byte
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pid uintptr
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ws unix.WaitStatus
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err error
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errno syscall.Errno
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)
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sourceP, err = syscall.BytePtrFromString(source)
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if err != nil {
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return err
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}
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targetP, err = syscall.BytePtrFromString(target)
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if err != nil {
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return err
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}
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fstypeP, err = syscall.BytePtrFromString(fstype)
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if err != nil {
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return err
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}
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if data != "" {
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dataP, err = syscall.BytePtrFromString(data)
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if err != nil {
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return err
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}
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}
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runtime.LockOSThread()
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defer runtime.UnlockOSThread()
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pid, errno = forkAndMountat(dirfd,
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uintptr(unsafe.Pointer(sourceP)),
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uintptr(unsafe.Pointer(targetP)),
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uintptr(unsafe.Pointer(fstypeP)),
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flags,
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uintptr(unsafe.Pointer(dataP)))
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if errno != 0 {
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return errors.Wrap(errno, "failed to fork thread")
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}
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_, err = unix.Wait4(int(pid), &ws, 0, nil)
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for err == syscall.EINTR {
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_, err = unix.Wait4(int(pid), &ws, 0, nil)
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}
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if err != nil {
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return errors.Wrapf(err, "failed to find pid=%d process", pid)
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}
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errno = syscall.Errno(ws.ExitStatus())
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if errno != 0 {
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return errors.Wrap(errno, "failed to mount")
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}
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return nil
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}
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// forkAndMountat will fork thread, change working dir and mount.
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//
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// precondition: the runtime OS thread must be locked.
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func forkAndMountat(dirfd uintptr, source, target, fstype, flags, data uintptr) (pid uintptr, errno syscall.Errno) {
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// block signal during clone
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beforeFork()
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// the cloned thread shares the open file descriptor, but the thread
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// never be reused by runtime.
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pid, _, errno = syscall.RawSyscall6(syscall.SYS_CLONE, uintptr(syscall.SIGCHLD)|syscall.CLONE_FILES, 0, 0, 0, 0, 0)
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if errno != 0 || pid != 0 {
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// restore all signals
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afterFork()
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return
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}
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// restore all signals
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afterForkInChild()
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// change working dir
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_, _, errno = syscall.RawSyscall(syscall.SYS_FCHDIR, dirfd, 0, 0)
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if errno != 0 {
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goto childerr
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}
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_, _, errno = syscall.RawSyscall6(syscall.SYS_MOUNT, source, target, fstype, flags, data, 0)
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childerr:
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syscall.RawSyscall(syscall.SYS_EXIT, uintptr(errno), 0, 0)
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panic("unreachable")
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}
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